Hydrolysis of calcium carbide yields ethyne.
$$CaC_{2} + 2H_{2}O \rightarrow C_{2}H_{2} + Ca(OH)_{2}$$
Now, in the presence of red hot copper tube, $$3$$ molecules of ethyne polymerize to give benzene.
$$3C_{2}H_{2}$$ + red hot $$Cu$$ tube $$\rightarrow C_{6}H_{6}$$ (benzene)
In the presence of $$HNO_{3}-H_{2}SO_{4}$$, nitration of benzene occurs (electrophilic aromatic substitution) and nitrobenzene is formed.
$$C_{6}H_{6} + HNO_{3}-H_{2}SO_{4} \rightarrow C_{6}H_{5}NO_{2}$$ (nitrobenzene)
In the presence of $$Fe-HCl$$, nitrobenzene reduces to aniline.
$$C_{6}H_{5}NO_{2} + Fe-HCl \rightarrow C_{6}H_{5}NH_{2}$$ (aniline)
Aniline on reaction with $$NaNO_{2}-HCl$$ gives benzene diazonium chloride.
$$C_{6}H_{5}NH_{2} + NaNO_{2}-HCl \rightarrow C_{6}H_{5}N_{2}^{+}Cl^{-}$$
The complete reaction sequence is as follows:
$${ CaC }_{ 2 }\xrightarrow { Hydrolysis } C_2H_2\xrightarrow [ Cu\:tube ]{ Red\:hot } C_6H_6\xrightarrow [ { 50-60 }^{ 0 }C ]{ { HNO }_{ 3 }-{ H }_{ 2 }{ SO }_{ 4 } } C_6H_5NO_2\xrightarrow { Fe+HCl } C_6H_5NH_2$$
$$ \xrightarrow {NaNO_2 + HCl,\: 0^oC} C_6H_5N_2^+Cl^-$$
Therefore, $$E$$ is benzene diazonium chloride.